Cleaning method



April 30, 1946.

B. J. SZATYN 2,399,267

CLEANING METHOD Filed July 2'7, 1940 V INVENTOR 62 gazes/4'11:

BY Z.

ji! z IATTO Ya.

Patented Apr. 30, 1946 UNITED STATES PATENT OFFICE CLEANING METHOD Boleslaus J. Szatyn, Detroit, Mich., assignor to Solventol Chemical Products, Inc., Detroit, Mich., a corporation of Michigan Application July 27, 1940, Serial No. 347,911

6 Claims.

,The present invention relates to cleaning proc- -ess es .and material and particularly such as are applicable to the cleaning of metal parts in the .process of manufacture in order to prepare their surfaces for such operations as plating, rust- Jproofing or-painting. This invention constitutes a;n-improvement upon one of the processes set forth in the application of Charles A. Campbell,

Serial No. 347,929, filed July 27, 1940.

:Inthe aforementioned application of Charles A. Campbell, there are disclosed materials, apparatus'ahd methods for conducting cleaning'oper- 'ations' on metal parts for the purpose of removing bufling and drawing compounds and other stubbom sticky, oily or greasy materials from metal .parts in order to prepare the surfaces for plating, rust-proofing or painting. In accordance with the campbellapplication, to which reference may be hadfor further details, the cleaning operation is carried on by the use of an unstable mixture of a cleaning solvent emulsion and an unemulsified cleaning solvent. This type of cleaning material is exceedingly effective, particularly in spray cleaning, but it is found that after a certain period of use when removing soil containing emulsifying agents there is a tendency of the unstable cleaning bath to form a stable emulsion which is much less efiective as a cleaning agent. Accordingly, it is an object of the present invention to overcome this difliculty by maintaining the cleaning bath in an unstable form for a greater length of time than would otherwise be possible in order to prolong the period at which the cleaning bath has its maximum efliciency.

Another object of the present invention is'to provide means for changing the form of the greasy or sticky materials removed from the work being'cleaned to a form in which they will not adhere to work subsequently treated-in the cleaning bath.

Another object of the invention is to provide means to cause the greasy, sticky and other constituents of the soil or dirt to not only change form but. to leave the cleaning emulsion and float in the unemulsifled cleaning solvent layer in order to facilitate removal of such dirt or soil from the solvent to the end that the solvent may be re-used. Other objects and advantages of the invention will be come apparent from the following specification, the accompanying drawings, and the appended claims.

I e aw Eigure fl shows a horizontal section, taken on the-line 1+1 of Fig. 2;"of a spray washing ma.-

chine of a type adapted forluse in carrying .out the present invention; I s Fig. 2 shows a vertical section in thesame machine, taken on the line 2-2 ofFigure 1%,,

Fig. 3 is a sidelview'ona reduced? scale. 'taken on the line 3-3 of Fig.2, parts being brokena'way to show a portion of the interior 'of the machine. Fig. 4 is a view showing the manner in which the cleaning bath of thepresent invention" is employed in'dip cleaning. The cleaning method of the present invention is preferably carried out by a, spraying operatio in which an unstable mechanical mixtureiof a cleaning solvent emulsion and an unemulsified cleaning solvent are sprayed upon the workrto pe cleaned. This unstable mixturenisireferredfto throughout the specification. asfl'thejfbathg'fpr cleaning bat Thisbathis madeunofga sol.- vent emulsion containing any suitable cleaning solvent, water, and an emulsifyingagentsuclr as a soap. This portion of the bath, which isre; ferred to throughout as the emulsion; 'is a stable solvent and water emulsion having the property of being able to clean by wetting action and' dispersion. The cleaning bath, in addition to-.the

cleaning emulsion, contains solvent in'an amount V greater than can be emulsified with the cleaning emulsion, with the result that "the additional sol-.- vent remains separate from the emulsion and tends to float on the surface of the bath in ajlayer. This unemulsified solvent is normally, but not necessarily, the same as the solvent inthe emulsron. I v

A machine suitable for carrying out the. spray cleaning process is illustrated in the drawing- As there shown,the machine comprises a sheet metal casing of any desired constructionhaving side walls I0 and I l, top wall l2, and bottom wall l3. The lower portion of the casing has a projection at one side defined by an auxiliary sidewall I l spaced outwardly from the wall ll at the upper part of the machine on the same side. The offset between the .walls H and i4 is closed jby aplu rality of hingedlids l5, l6 and I1, The ends of the machine are partially closed'by end walls l8, which. are entirely closed at their lower portions but have, at their upper central portions, openings I! through which the work 'to be cleaned'is passed.

Any desired means for conveying the work through the machine may be utilized, but, as

shown in the drawing, it is preferred .to utilize a- 4. CLEANlNG AND UQUID CONTAL-E W I-i SST-LIBS (U55 Kiri-WWI esizlihtii how thereof. The chain conveyer, indicated generally at 22, is provided with a plurality of longitudinally spaced hooks 23 for supporting the work 24 to be cleaned.

The machine is divided into three compartments 25, 26, and 21. The compartment 25 is the washing compartment. Compartment 2B, which is the first rinsing stage, is separated from com- .partment 25 by a wall 28. Compartment 26, in

turn, is separated from compartment 27, the the distance between the top of the pipe and the second rinsing stage, by means of awall 29 similar interface was from four to six inches. It is, of to the wall 28. The walls 28 and 29 have opencourse, necessary to make additions to the bath ings 30 and 3| therein, which openings are similar from time to time to compensate for evaporation to the openings 19 in the end walls [8. The lower loss and the material which adheres to the work portions of the compartments 25, 26 and 21, which which otherwise might vary the level of the interare separated from each other by the lower porface. tions of the walls 28 and 29, form reservoirs for The two rinsing stages 26 and 21 are identical retaining the washing fluid and rinse water, reand each comprises a plurality of vertical rinsing spectively. That is, the lower portion of the comspray pipes 46 and 4'1, respectively, connected by partment forms a reservoir for the washing 2o suitable piping to the discharge side of individual fluid while the lower portions of compartments 26 pumps 48 and 49, respectively. The pump inlets and 21 form separate reservoirs for rinse water. 58 and 5| are connected directly to the rinse water Mounted in the compartment 25 adjacent the reservoirs in the lower parts of compartments 26 side walls H and I2 are a plurality of vertically and 27, so that the rinsewater is re-circulated. extending spray pipes 32 connected by suitable 25 Re-circulation of the rinse water is desirable not pi ing to the discharge outlet'36 of a pump as. o y e se it e s in a s v g r a e u The vertically extending spray pipes are provided also a saving of heat since the wateris spra ed at throughout their length with a plurality of spaced h p ed te pe tu e o t will be nozzles of any desired form, such as milled slots ted t at the l t W sh p ys 32 are 1 51- in the pipe, adapted to spray the cleaning mat 3o tioned quite l e o the fi n ng rays 46. rial upon the work carried by the chain con ing s pa a d ly by th all o pa titi n 28. veyer 22. It will be noted that the last spray pipes This s des b in O er to aVOid y drying O are positioned very close to the wall 28, with the 0f the Parts between e' 'sspray and result that the wall 28 forms a bafileacting to prethe first rinsing spr yvent the cleaning fluid from entering the first The Clea-hing bath in the reservoir of compartrinsing co partm t, merit 25, as well as the rinse water in the reser- The cleaning material which is discharged by V011 p ts 5 a d h s aintainedat the spray pipes 32 falls back into the reservoir the desired te pe a e, preferably .F-, y in the. bottom of the spray compartment 25 a d any suitable means such as thermostatically conmeans are provided for drawing the cleaning 40 trolled steam coils, not Shown, in the ott ms of material from this reservoir and conducting it the reservoirsto the intake of the pump 38. It will be noted, I11 Order to avoid Contamination of t e rinse' as shown in Fig. 2 of the drawing, that the cleanwater y the vapor om e w s s a a ing bath in the reservoir comprises an underlying for the further P po Of preventing 105$ of body of emulsion indicated '40 upon t top of cleaning material due to evaporation, there is prowhich is a layer 42 of unemulsified solvent. These Vided a circulating d Condensing y e S own two immiscible liquids have a distinct interface best in AS there Shown, there s P ided the level of which is indicated by the line 43 in an air conduit 54 leading fr m t e op of t e Fig. 2. It is necessary, in order to properly conmachine casing at a point 011 the Washing duct the washing operation [30 draw into pump 38 partment Side Of partition 28, as shown in dotted mixture of these two immiscible fluid and this lines in Fig. 1.. The conduit 54 leads to the intake is accomplished in the machine illustrated in the of fan 56, Which d arges i to a conduit 5'! drawing by connecting the pump intake 44 to a leading back t t e p o e Casing t P nt pipe 45, the open end of which extends vertically just inside of the entering end wall It, also shown and lies just below the interface 43 of the two 55 in dotted-111165111 Y Withdrawing oil d liquids. As a result of this arrangement, the vapor m a p t d t t b t on t e was pump suction draws in part upon the solvent layer compartment Side Of the p n 39 in Partition 42 and in part from the underlying emulsion layer 23, fiOW f air f om the rinsing compartment 40, t drawing in a mechanical mixture of the into the washing compartment is created, which is two immiscible liquids. The action of the pump, effective to prevent entry of the vapor from the as well as the turbulence created by the spray, Washing p ay to the rinsing compa srenders this mechanical mixture an exceedingly leading t V por and air back through t e dis- 'intimate one, with the result that the free or un- Charge u t 5 into the Opposite end of t e emulsified solvent is thoroughly dispersed Washing Compartment. y of the VaDOr Which through the spray. has condensed will be returned to the cleaning Aside from the simplicity of this method of bath and a certain amount of the uncondensed mixing the two layers, the method has the further V p i a y When Coming in Contact with e advantage in that the relative proportions of the washing spray will likewise be condensed. A portwo liquids may be readily varied in any given tion of the balance may flow outwardly through installation by varying the distance between the the opening l9 in the end wall l8, while the rest top of pipe 45 and the interface 43, or, in other Will flow towards the inlet pipe 54. By placing a words, by adjusting the level of the interface. condenser, shown more or less diagrammatically This may be done readily, since the system is aat 60, in the inlet pipe 54, it is possible to condense closed one, by varying the quantity and propora greater portion of the vapors drawn into the tions of the cleaning bath in the reservoir.

The ratio of the amounts of the two liquids, which are drawn into the pump, is a function of the pump capacity, the intake pipe diameter, and the distance between the top of the pipe -and the interface. These three factors may, of course, be adjusted to produce any desired ratio. Excellent results have been secured in an installation in which the pump capacity was 500 gallons per minute, the intake pipe diameter was four inches, and

pipe 54. As a result, loss of cleaning fluid is fur flow from the rinse tanks. rangement and proportions of the washing maj chine are not critical as it is possible to utilize a 1 longer machine or one which is arranged in gen- 'ther reduced. The form of condenser shown is I of the water cooled type utilizing a source of water which enters the condenser from a pipe 62 and is discharged through pipe 63. It is preferable to constantly overflow the rinse tanks in order to remove any dirt or foreign material that may collect as a scum on the surface, and, therefore, it is advantageous to run the condensing water from pipe 63 directly into the rinse water reservoirs.

This may be done in any desired manner, such as that indicated by the dotted line pipes 64 and 65 in Fig. 3. Suitable means, such as the two overflow pipes 66 and 61, may be provided to take the over- The Darticularareral, U-shape instead of being arranged in astraight line, and any desired'number and arrangement of washing and rinsing sprays may be utilized.

While the solvent emulsion and the unemulsified solvent are intermixed in the spray, the

fact that they are simply a mechanical mixture and not a stable emulsion enables the two constituents to act more or less independently, although simultaneously, upon the soil to be removed from the parts. The solvent in the spray has superior penetrating and wetting properties, with the result that it penetrated even the most heavily caked material and coats or wets the inert constituents. This coating or wetting by the which greatly facilitates rinsing.

In some cases, for example, where it is necessary to remove heavily caked bufling compounds from zinc die castings preparatory to electroplating, it is advisable to use both the dip and spray cleaning methods in succession. In this combination process, the parts to be cleaned are first dipped in a still bath containing the emulsion upon which is a layer of unemulsified solvent. This bath, as set forth in greater detail in the aforementioned Campbell application may be the same as the spra bath, except that it should contain less water. The dipping operation, as shown in Fig. 4, is carried on in an open tank which contains the cleaning bath. The bath is made up of two layers; namely, the emulsion layer 16 and the solvent layer T! overlying the emulsion with an interface 19 between the two. The

manner, as by hooks 18, is lowered into the bath entirely through the solvent layer and into the body of the emulsion and then withdrawn.

After the parts are dipped into this still bath, entirely through the solvent layer, they are then subject to a spray cleaning operation without any intermediate rinse. The spray cleaning operation should be conducted on the part before it has time to dry, although it is found that the cleaning emulsion from the dip bath tends to prevent or retard drying for a reasonable interval between the two washing operations, with the result that a it possible to have an intervening interval of severalminutes. When the cleaning bath of the aforementioned p m l siiiie used r re v d 'work 24, which may be supported in any desired narybufiing or drawing compounds, the material removed from the parts to be cleaned gradually contaminates the cleaning bath' and reduces its efiiciency. The most serious contamination is caused by the greasy or soapy constituents which find their way into the cleaning bath, since some of them act as emulsifying agents and gradually increase the capacity of the bath to emulsify the excess solvent. Accordingly, as the baths are used continuously the excess solvent which initially floats upon the bath in a separate clear layer is gradually emulsified with the cleaning emulsion beneath, and the free solvent layer reduces in amount until eventually it entirely disappears, all of the solvent-having been emulsified with the cleaning emulsion. As soon as the bath becomes a complete stable emulsion, its cleaning efficiency is greatly reduced.

The periodof time required for the cleaning bath to reach this completely emulsified stage depends upon the amount of cleaning which is done, the initial size of the bath, the proportion of solvent initially present, and the amount of soapy or emulsifying agents in the dirt or soil which is being removed from the parts to be cleaned. Under severe conditions, the bath may become completely emulsified in from four to eight hours. When this occurs, the bath should no longer be used. c.

In accordance with the present invention, the period during whichthe bath may be used at maximum efiiciency is/greatly prolonged, and

other important advantages secured, by maintaining the cleaning" .emulsi on in an acid condition and controlling the acidity-within certain welledeflned limits. Thus, in one case, when sufiicientacid or acid reacting salt was added to the cleaning emulsion to maintain a pH in the order of 2.5 -to.3.5, the useful life of the bath was increased from four to thirty-two hours.

Maintenance of an acid condition of the cleaning emulsion produces a number of important results. First, it prevents emulsification of the excess -solvent by the emulsifying elements of the material removed from the work; second, it prevents a permanent colloidal dispersion of the dispersible elements of the soil in the cleaning emulsion which would load the emulsion and decrease its dispersing or cleaning power; and, third, it reacts with the dispersible substances to change them into a relatively hard, non-sticky form in which they will not adhere to the work,

and in which they will not enter into objectionable reactions with the work. This change in consistency isapparently effected without causing the particles to drop or release the inert materials carried by or embedded in them. In addition, it is found that the small particles ofdispersible material, which have been reacted upon by the acid, tend to float iii the solvent layer and thus do not contaminate the cleaning emulsion. These particles are not affected by the solvent andhence do no harm, even though present in relatively large amounts. On the other hand, when the bath has served its useful life, the solvent layer may be drawn ofi and reclaimed in any suitablefonn of settling tank. The solvent is in relatively pure condition since, except for the relatively hard non-sticky particles which float in it'and can be readily removed, byskimming or other mechanical separating methods,

it contains only a relatively small quantity of completely dissolved oils or greases which were removed from the work. a

The above describedacid treatment cannot be used in a dip washing method. on chemically active metals, such as die cast alloys, because of the fact that the acid in the cleaning emulsion will etch the metal parts in production. For some reason, not entirely understood, this etching may be eliminated in the spray washing method, even, though an exceedingly chemically active metal, such as zinc, is being cleaned. Apparently, this is due to a blanketing of the metal by a film of unemulsified solvent in which there is no acid. At least, it is noted that if,

under any given conditions, etching occurs in the acidified spray cleaning operation, it can be eliminated without changing the pH either by increasing the amount of solvent in the bath or by dipping the work either in pure solvent or the regular bath immediately before the spray cleaning operation, or by both of these expedients.

In addition, temperature plays an important part in the tendency of the acid to attack the metal, and it is noted that there is much less likelihood of acid attack at the temperature of 120 R, which is preferred, than at higher temperatures.

Except for the acid strength, which is critical, the particular ingredients to be used in accordance with the cleaning method outlined may be widely varied, as may the proportions of .the materials used. These variations depend in any particular case upon the nature of the cleaning operation to be carried on andother factors, As a general guide, a number of specific examples are hereafter given, along with an indication of the factors influencing the choice of constituents as well as the relative proportions of the various ingredients.

While, as previously indicated, the cleaning emulsion is a cleaning solvent and water emulsion formed by any suitable soap or other emulsifying agent, it is preferred to use as the emulsifying agent an amine soap formed from oleic acid, since such soaps have excellent wetting and penetrating properties and, in addition, are soluble in oils which, for reasons to be pointed out hereafter, is an advantage.

The solvent constituent of the solvent emulsion is preferably largely made up of the same solvent which forms the unemulsified solvent layer of the cleaning bath. Excellent results have been secured with a mineral spirit solvent falling between kerosene and naptha in volatility, but any other cleaning solvent may be used. Other solvents which may be used include kerosene, naptha, or any solvent that will dissolve oil and grease. It is apparent, also, that any desired combinations of solvents may be used.

It is preferred to use, in addition to the solvent, a smaller quantity of pine oil, since pine oil (steam distilled) has good wetting and penetrating properties and is an effective flotation agent which will assist flotation of the particles of acid reacted dispersible material.

In order to make available for sale and shipment a mixture of all of the ingredients (excepting water and acidifiers) necessary to carry on the process, it is preferred to combine the soap and solvent constituents, including oil, if any is present, in a clear stable solution, so that no settling or layering of the material will occur prior to use. It is partly for this reason that the use of an amine soap is preferred, since soaps of this type are soluble in hydrocarbon solvents and oils to a certain extent. In addition, if necessary, a suitable coupling or blending agent such as ethylene glycol monobutyl ether or cyclohexanol may be used to bring the soap and oil and solvent constituents into a stable solution. The pine oil itself acts to a certain extent as a blending agent. It is obvious that various proportions and ingredients may be used, but, as an example, one satisfactory formula is as follows:

' The above mixture of ingredients forms a clear amber solution which is permanently stable and which, therefore, is ready for addition to a suit able quantity of water for use at any time.- It contains not only the solvent and emulsifying agent necessary to form the emulsion, but also the excess solvent necessary in the cleaning bath. It may be combined with any desired amount of water up to onepart of solution to fifty parts of water, and when so combined with water hecomes an unstable mixture of the cleaning emulsion and excess solvent. A certain percentage of the pine oil and mineral spirit solvent in the above mixture goes into the emulsion, but a substantial percentage of both of these ingredients simply remains on top of the bath as a clean unemulsifled layer. .The amount of solvent in the solution does not appear to be-critica1 except secured.

The amount of water which should be added to the above solution depends upon the conditions and the type of cleaning operation being conducted. In the spray method, excellent results have been secured with thirty to forty parts of water to one part of either the above solution or a half and half mixture of that solution and reclaimed solvent. These proportions, however, do not appear to be very critical, except, as previously indicated, in the spray cleaning method it is generally necessary in any given case to adjust the proportions of water and solution in the cleaning spray by experiment in order to avoid etching of the metal when acid is used in the emulsion. In the case of the preliminary dip bath, previously mentioned, the above solution may be combined with as little as 4 parts of water to one of solution. No acid should be used in the dip bath because it is apt to attack the parts being cleaned.

So far as the acid treatment is concerned, it

may be carried on by any water soluble acid or acid reacting salt capable of producing a solution or a cleaning emulsion having the desired pH. Among the inorganic acids which may be used successfullyare sulphuric acid, phosphoric acid, pyrophosphoric acid and phosphorous acid. Nitric, hydrochloric and acetic acids cannot be used because they are too volatile and cause obnoxious or poisonous fumes at F. Among the organic acids which may be used successfully are oxalic acid, maleic acid, monochloro acetic acid, dichloro acetic acid, bromoacetic acid, and phthalic acid. Formic acid cannot'be used be cause it is too volatile at 120, and trichloro acetic acid, which is otherwise satisfactory, is inconvenient to use because its hygroscopic character makes handling diflicult. In addition to the above acids, certain inorganic salts which ionize or hydrolyze to give an acid solution may also be used. For example, sodium bisulphate and potassium bisulphate, which ionize to give an acid solution, may be used satisfactorily to produce a cleaning emulsion having the desired pH. Aluminum sulphate, which both ionizes and then hydrolyzes to give an acid reaction, can be used, although when used alone will produce a minimum pH of only 3.5, which is not suificiently low for most purposes. It is obvious, also, that mixtures of any of the above acids and/ or salts may be used if desired.

The pH of the cleaning emulsion can be varied as desired to fit the requirements of the particular cleaning operation under consideration. It is found, for example, that in removing buifing compounds from zinc die castings a pH of 3.5 is sufiicient to prevent emulsification of the bath, but that a greater acidity, namely, a pH of 2.0 to 3.3, is necessary to causean acid reaction on the dispersible material in order to throw it out of the cleaning emulsion and render it nonsticky in character. In cleaning zinc die castings, any greater acidity (or lower pH) than a pH of 2.0 was found in a number of instances to result in etching and the production of an invisible film or surface condition on the metal that interfered with plating operations. It is sometimes necessary to employ a higher pH than 2.0 to avoid difiiculty. The minimum and maximum pH for the solution when cleaning different metals and with various proportions of the cleaning bath may be readily determined by experiment in accordance with the foregoing principles. Likewise, the frequency with which acid additions to the bath must be made depends upon the conditions and must be determined by experiment. In one case in which zinc die castings were being treated to remove bufling compound, acid additions were made every four hours in amounts suflicient to bring the pH to about 2.5, with excellent results. In another, hourly additions sufiicient to bring the acidity to a pH of about 2.5 produced even better results.

In the appended claims, the term emulsion" is used to refer to a stable emulsion or colloidal suspension of water and some other immiscible liquid in the presence of an emulsifying agent such as a soap or the like. The term solvent is used to refer to cleaning solvent liquids adapted to dissolve greases and oils and other similar materials.

While several embodiments and examples of the present invention are given, it will be understood that changes may be made in the apparatus, methods, various ingredients and proportions without departing from the spirit of the invention or the scope of the appended claims.

What is claimed is:

1. The method of cleaning metal parts for the purpose of removing matter containing emulsifying agents which comprises spraying the parts with a mechanically combined unstable mixture of an emulsion of grease solvent and water and an unemulsified excess of said solvent, collecting, re-mixing, and re-circulating said mixture through the cleaning spray, and maintaining said emulsion in an acid condition.

The method of cleaning metal parts in the course of manufacture which comprises spraying the parts with a mechanically combined unstable mixture of an emulsion of grease solvent and water and an unemulsified excess of said cleaning solvent, collecting, re-mixing, and recirculating said mixture through the cleaning spray, and maintaining the pH of said emulsion approximately within the range of 2.0-3.5.

3. The method of removing hufling compounds from metal parts containing zinc in preparation for electroplating such parts which comprises dipping said parts into a grease solvent and thereafter spraying the parts with a mechanically combined unstable mixture of an emulsion of rease solvent and water and an unemulsified excess of said solvent, collecting, re-mixing, and re-circulating said mixture through the cleaning spray, and maintaining the pH of said emulsion at a point within the range of approximately 2.0 to 3.5.

4. The method of removing bufiing compounds from metal parts containing zinc in preparation for electroplating such parts which comprises dipping said parts into an emulsion of grease solvent and water and thereafter spraying the parts with a mechanically combined unstable mixture of an emulsion of grease solvent and water and an unemulsified excess of said solvent, collecting, re-mixing, and re-circulating said mixture through the cleaning spray, and maintaining the pH of said emulsion at a point within the range of approximately 2.0 to 3.5.

5. The method of removing bufiing compounds from metal parts containing zinc in preparation for electroplating such parts which comprises dipping said parts into an unstable mixture of an emulsion of grease solvent and water and an unemulsified solvent until the parts are entirely within the body of emulsion underlying the top solvent layer, withdrawing said parts and thereafter spraying the parts with a mechanically combined unstable mixture of an emulsion of grease solvent and water and an unemulsified excess of said solvent, collecting, re-mixing, and re-circulating said mixture through the cleaning spray, and maintaining the pH of said emulsion at a point within the range of approximately 2.0 to 3.5.

6. The method of cleaning metal articles which comprises spraying the articles with a mechanically combined unstable mixture of an unemulsifled grease solvent which is of less density than 

